1. Field of the Invention
The present invention relates to a method (process) for preparing certain 2,2-difluoroethylamine derivatives starting from 2,2-difluoroethylamine.
2. Description of Related Art
2,2-Difluoroethylamine derivatives are useful intermediates for preparing active agrochemical ingredients (see WO 2007/115644). Various methods for preparing 2,2-difluoroethylamine derivatives known.
WO 2009/036900, for example, describes a method for preparing 2,2-difluoroethylamine derivatives by amide hydrogenation of N-[(6-chloropyridin-3-yl)methyl]-2,2-difluoroacetamide (scheme 1).

This method is unfavourable due to the use of complex hydrides such as sodium borohydride, since hydrides are expensive to use and raise safety concerns.
WO 2009/036901 describes the reduction of N-(6-chloropyridin-3-yl)methylene-2,2-difluoroethanamine by hydrogen (scheme 2).

This method is unfavourable due to the use of hydrogen, since the use of hydrogen raises considerable safety concerns here to.
WO 2011/157650 describes the preparation of 2,2-difluoroethanamine derivatives starting from 2,2-difluoro-1-haloethanes with primary amines in the presence of organic bases (scheme 3).

The disadvantage of this method is that the reaction must be carried out in a high-pressure apparatus (autoclave).
The patent publication WO 2007/115644, which is concerned with the preparation of insecticidally active 4-aminobut-2-enolide compounds, describes the preparation of compounds of the general formula A-CH2—NH—R1, in which A represents specific heterocycles and R1 is haloalkyl, by alkylation of the nitrogen (scheme 4).

WO2007/115644 specifically describes the preparation of N-[(6-chloropyridin-3-yl)methyl]-2,2-difluoroethan-1-amine (compound (3), which is synthesized starting from 2-chloro-5-chloromethylpyridine (compound (2)) and 2,2-difluoroethan-1-amine (compound 1)) in the presence of triethylamine (see scheme 5)). In this case, the compounds (1), (2) and triethylamine are used in equimolar amounts. The desired product is obtained in a yield of 53%.

The method described in WO 2007/116544 for preparing compounds of the formula A-CH2—NH—R1, in which A represents specific heterocycles and R1 is haloalkyl, is disadvantageous since polyalkylation of the nitrogen can occur during the reaction. This leads to a loss of yield, which can be seen also in the yield of the specifically cited example. The yield was only 53%. These polyalkylations can only be reduced by the use of a large excess of amine. The distillative recovery of the costly amine, however, is generally laborious and not without loss.
Due to the significance of 2,2-difluoroethylamine derivatives as building blocks for synthesizing active agrochemical ingredients, it is, however, necessary to find a method which can be used economically on an industrial scale. It is also desirable to obtain the specific 2,2-difluoroethylamine derivatives with high yield and high purity, such that the target compound preferably does not have to be subjected to any further potentially complex purification.
A method has now been found for preparing certain 2,2-difluoroethylamine derivatives which avoids the disadvantages of the known methods and moreover is simple and economic to carry out, such that it can be used industrially.